[unix-history] / usr / man / man1 / compact.1

.TH COMPACT 1 3/15/79
.UC
.SH NAME
compact \- compress files
.SH SYNOPSIS
.B compact
[ name ... ]
.SH DESCRIPTION
.I Compact
compresses the named files using an adaptive
Huffman code.  If no file names are given,
then the standard input is compacted to
the standard output.
Unlike
.I pack,
.I compact
operates as an on-line algorithm.
Each time a byte is read,
it is encoded immediately
according to the current prefix
code.
This code is an optimal Huffman code
for the set of frequencies seen so far.
It is unnecessary to prepend a decoding
tree to the compressed file (as in
.I pack
\b), since the encoder (\b
.I compact
\b) and the decoder (\b
.I uncompact
\b) start in the same state and stay
synchronized.
Furthermore,
.I compact
and
.I uncompact
can operate as filters.
In particular,
.sp
	... | compact | uncompact | ...
.br
.sp
operates as a (very slow) no-op.
When an argument
.I file
is given,
it is compacted
and the resulting file is placed in
.I file.C;
.I file
is unlinked.
The first two bytes of the
compacted file code the
fact that the file is compacted.
This code is used to prohibit
recompaction.
.sp
The amount of compression
to be expected depends
on the type of file being compressed.
Typical values of compression are:
Text (38%), Pascal Source (43%),
C Source (36%) and Binary (19%).
These values are the percentages
of file bytes reduced.
.SH RESTRICTIONS
The last segment of the filename must
contain fewer than thirteen characters
to allow space for the appended '.C'.
Directories cannot (and should not)
be compressed.
.SH DIAGNOSTICS
Compact will not compress directories.
Also messages about unopenable files, etc.
No attempt will be made to compress files
which have already been compressed by
either compact or pack.
.SH FILES
 .C files created
.br
Input files unlinked (unless protected)
.SH "SEE ALSO"
uncompact (1),
ccat (1)
.sp
Gallager, Robert G., "Variations on a Theme by Huffman",
.I I.E.E.E.
.I Transactions
.I on
.I Information
.I Theory,
vol. IT-24, no. 6, November 1978, pp. 668 - 674.
.SH AUTHOR
Colin L. Mc Master
.SH BUGS
Commit	Line	Data
4df0b004 CMM	1	.TH COMPACT 1 3/15/79
	2	.UC
	3	.SH NAME
	4	compact \- compress files
	5	.SH SYNOPSIS
	6	.B compact
	7	[ name ... ]
	8	.SH DESCRIPTION
	9	.I Compact
	10	compresses the named files using an adaptive
	11	Huffman code. If no file names are given,
	12	then the standard input is compacted to
	13	the standard output.
	14	Unlike
	15	.I pack,
	16	.I compact
	17	operates as an on-line algorithm.
	18	Each time a byte is read,
	19	it is encoded immediately
	20	according to the current prefix
	21	code.
	22	This code is an optimal Huffman code
	23	for the set of frequencies seen so far.
	24	It is unnecessary to prepend a decoding
	25	tree to the compressed file (as in
	26	.I pack
	27	\b), since the encoder (\b
	28	.I compact
	29	\b) and the decoder (\b
	30	.I uncompact
	31	\b) start in the same state and stay
	32	synchronized.
	33	Furthermore,
	34	.I compact
	35	and
	36	.I uncompact
	37	can operate as filters.
	38	In particular,
	39	.sp
	40	... \| compact \| uncompact \| ...
	41	.br
	42	.sp
	43	operates as a (very slow) no-op.
	44	When an argument
	45	.I file
	46	is given,
	47	it is compacted
	48	and the resulting file is placed in
	49	.I file.C;
	50	.I file
	51	is unlinked.
	52	The first two bytes of the
	53	compacted file code the
	54	fact that the file is compacted.
	55	This code is used to prohibit
	56	recompaction.
	57	.sp
	58	The amount of compression
	59	to be expected depends
	60	on the type of file being compressed.
	61	Typical values of compression are:
	62	Text (38%), Pascal Source (43%),
	63	C Source (36%) and Binary (19%).
	64	These values are the percentages
65	of file bytes reduced.
66	.SH RESTRICTIONS
67	The last segment of the filename must
68	contain fewer than thirteen characters
69	to allow space for the appended '.C'.
70	Directories cannot (and should not)
71	be compressed.
72	.SH DIAGNOSTICS
73	Compact will not compress directories.
74	Also messages about unopenable files, etc.
75	No attempt will be made to compress files
76	which have already been compressed by
77	either compact or pack.
78	.SH FILES
79	.C files created
80	.br
81	Input files unlinked (unless protected)
82	.SH "SEE ALSO"
83	uncompact (1),
84	ccat (1)
85	.sp
86	Gallager, Robert G., "Variations on a Theme by Huffman",
87	.I I.E.E.E.
88	.I Transactions
89	.I on
90	.I Information
91	.I Theory,
92	vol. IT-24, no. 6, November 1978, pp. 668 - 674.
93	.SH AUTHOR
94	Colin L. Mc Master
95	.SH BUGS